1. Field of the Invention
The present invention relates to a stent. More particularly, it relates a low profile highly expandable stent.
2. Description of the Prior Art
Stents for use in transluminal implantation are known in the prior art. Most are known to be balloon expandable, self-expandable, or thermally expandable. But, the degree of expansion in these prior art stents are determined by the diameter of the balloon used to cause the expansion or of the diameter of an artery when using self-expanding or thermally expanding means. An improved stent is needed in which the degree of expansion in the stent is not constrained by diameter of the balloon or of the artery.
Some prior art stents are known to comprise rigid and flexible portions. U.S. Pat. No. 5,383,892 (""892) to Cardon et al. disclose a stent employing at least two cylindrical rigid parts and at least one flexible part where the flexible part is welded to the rigid parts. Such a stent could be considered a combination stent utilizing a graft or other material. The invention of ""892 is adapted such that the rigid parts expand radially in a plastic manner and flexible parts expand radially in an elastic manner. Unfortunately, the degree of expansion of the ""892 stent is determined by the balloon used to expand the stent or the elastic nature of the metal used on the rigid parts. Such prior art stents are very limited in their degree of expansion and are not capable of the high degree of expansion seen in the stent of the present invention. In such a stent, it is necessary to form the stent having a very large profile, so that the higher degree of expansion can be achieved. However, large profile stents are not desirable due to the fact that they can not be used in minimally evasive surgical procedures. Requiring large incisions in the body and the artery only acts to complicate the surgical procedure and adds additional risk to the patient.
An improved stent is needed that utilizes combination stent-graft techniques and is capable of a high degree of expansion, yet retain a low profile so that surgeons can perform minimally evasive surgical procedures and use such novel stent in a wide range of artery diameters. Such improved stent can be manufactured in one size, yet be used universally.
The present invention relates to a low profile highly expandable stent. The present invention includes the following interrelated objects, aspects and features:
(1) In a first aspect, the present invention contemplates a stent having a low profile and with structure permitting expansion multiple times its original diameter. For example, the stent may expand from its initial diameter of approximately 1.5 millimeters to up to 12 millimeters.
(2) In a first embodiment of the present invention, a sheet of a material known as NITINOL is cut to form two end pieces having longitudinal slits and interconnected with serpentine connecting pieces. The longitudinal slits in the end pieces permit radial expansion of the stent while the serpentine nature of the connecting pieces allows longitudinal expansion. When the sheet has been appropriately cut into the end pieces with their connecting pieces, the end pieces are rolled into cylindrical tubes with their ends interconnected to form a tubular stent structure. A piece of tubular, preferably knitted, fabric is attached to the NITINOL material structure to form a finished stent. In one embodiment, the fabric is mounted within the NITINOL material. In another embodiment, the fabric is mounted outside the NITINOL material.
(3) In a further embodiment, only the NITINOL material end pieces are provided with the fabric material interconnecting them. In another embodiment, the fabric material is provided and only the NITINOL material connecting pieces are mounted in circumferentially spaced relation about the circumference of the fabric material.
(4) In an alternate embodiment, a tubular piece of material is substituted for the sheet of material. The end piece slits are formed by making small cuts in the material; in other words, material is not removed. The serpentine connecting pieces are then formed by removing material from the tubular piece of material through the use of a laser cutting machine, a chemical etching machine, an electron beam cutting machine or any other suitable device. The tubular fabric may then be mounted on the inside or outside of the serpentine connecting pieces.
(5) In any of the embodiments of the present invention, the stent is conveyed to the location of application in a collapsed configuration and is expanded in place in any suitable manner such as through inflation of a balloon catheter therewithin or by use of thermal expansion.
Accordingly, it is a first object of the present invention to provide a low profile highly expandable stent.
It is a further object of the present invention to provide such a stent including end pieces and/or connecting pieces made of a NITINOL material.
It is a further object of the present invention to provide such a stent including a tubular piece of fabric mounted either within or surrounding the NITINOL material structure.
It is a still further object of the present invention to provide such a stent with longitudinal slits in the end pieces thereof and with the connecting pieces made in a serpentine configuration.
These and other objects, aspects and features of the present invention will be better understood from the following detailed description of the preferred embodiments when read in conjunction with the appended drawing figures.